MEKK1 has been linked to cellular events such as NE-kappaB activation, inhibition of RXR-rnediated transcription, apoptosis, cell cycle control, and cell motility. MEKK1 has diverse modes of regulation, exists in multi-protein complexes, and induces variety of interdependent functions. Dr. Cobb wishes to assemble a picture that explains the diverse regulation, interactions, and functions of MEKK1. Thus she proposes the following aims. 1) She will analyze MEKK1 complexes using biochemical and molecular biological strategies. First, The principal investigator will isolate MEKK1 variants that are deficient in binding to interacting proteins. MEKK1 point mutations that fail to bind to targets will help to determine the functions of these interactions. To understand mechanisms that couple MEKK1 to its downstream targets, Dr. Cobb will characterize MEKK1 complexes, identify proteins in the complexes, and determine if the complexes change in amount or composition as a function of cell stimulation. 2) The principal investigator will determine effects of phosphorylation and protein-protein interactions on MEKK1 activity. MEKK1 is phosphorylated on numerous sites, and at least three protein kinases have been implicated upstream. She has identified two regions of MEKK1 that homo-oligomerize in vitro. The principal investigator will investigate the role of self-association on MEKK1 activity. 3) She will investigate the linkage between MEKK1 and the cytoskeleton. MEKK1 is localized to the cytoskeleton and activated by agents that impact cytoskeletal structure. The principal investigator will determine if blocking the interaction of MEKK1 with cytoskeletal elements interferes with its activation or signaling to downstream effectors. 4) The principal investigator will probe MEKK1 structure/function relationships using a cell migration assay. In cells lacking MEKK1, migration is impaired. The MEKK1 gene will be disrupted in the DT40B cell line, so that the principal investigator can use gene replacement to study its functions.